With a refractometer, a refractive index of a substance can be measured. The refractive index of a substance or sample depends from both, the wavelength of the light and from its temperature. In order to make measuring results comparable, in refractometers it is thus measured at specified wavelengths and temperatures. Deviations from standardized wavelengths or temperatures during measuring lead to measuring errors. In addition, there are measuring errors of the sensor system which are specific for the respectively related measuring principle. An example are mechanical changes which misadjust the optical set-up.
Relevant prior art is disclosed in U.S. Pat. No. 7,030,989, U.S. Pat. No. 7,492,447, U.S. Pat. No. 8,760,640, U.S. Pat. No. 5,729,347 and DE 10 2009 033 979.